This invention relates to a wireless base station with an array antenna and, more particularly, to such a base station that executes weighting the elements of the array antenna at a high speed.
Spatial domain multiplexing (SDM) is a technique by which a base station transmits signals to multiple terminals concurrently at a same frequency. In the space domain multiplexing, three prior art techniques are known as methods of scheduling without decreasing throughputs.
A first related art technique is a scheduling method described in Ohfuji et al. “Examining a Scheduling Method for Transmitting Multi-Directional Beams for Downlink High-Speed Packet Transmission” presented on Sep. 13, 2002 at the 2002 IEICE (the Institute of Electronics, Information and Communication Engineers) Society Conference B-5-88.
The base station predicts channel throughputs, using channel state information received from terminals, and sets a terminal having the greatest throughput as a first terminal. The base station calculates an antenna pattern for the first terminal.
Then, the base station selects any other terminal and calculates an antenna pattern for that terminal. The base station sets a terminal for which the array gain in the direction of the selected terminal in the antenna pattern for the first terminal is under threshold and the array gain in the direction of the first terminal in the antenna pattern for the selected terminal is under threshold as a second terminal candidate. The base station repeats this operation for all terminals and determines second terminal candidates.
The base station predicts channel throughputs from the channel state information from the terminals taken as the second terminal candidates and sets a terminal with the greatest predicted throughput as a second terminal. The technique in which the base station schedules transmissions at the same frequency to a plurality of terminals in this way is known.
A second related art technique is a scheduling method described in JP 2003-110485A.
The base station divides terminals with which it communicates into groups. The groups are set up so that the terminals in a group are less interfering with each other. The base station calculates the sum of channel throughputs for the terminals per group and schedules transmissions to the terminals in the group having the greatest sum of the channel throughputs. Such scheduling technique is known.
A third related art technique is a scheduling method described in JP 2003-110486A.
The base station sets a terminal having the greatest channel throughput as a first terminal, as in the first related art technique described above. The base station sets a terminal whose estimated bearing is more than a given angle from the first station as a second terminal. Such scheduling technique is known.